1. Field of the Invention
This invention relates to a laser apparatus. The present invention also relates to a gyro apparatus and, more particularly, it relates to a gyro utilizing a semiconductor laser.
2. Related Background Art
Known gyros for detecting the angular velocity of a moving object include mechanical gyros comprising a rotor or an oscillator as well as optical gyros. Particularly, optical gyros are bringing forth technological innovations in the field of gyro technologies due to their remarkable advantages including that they can start to operate instantaneously and show a broad dynamic range. Various optical gyros are known to date including ring laser type gyros, optical fiber gyros and passive type ring resonator gyros. Of these, the ring laser type gyro that utilizes a gas laser is the earliest comer and gyros of this type are popularly used in aeroplanes at present. In recent years, small and highly sophisticated semiconductor laser gyros that are formed on a semiconductor substrate have been proposed. See, inter alia, Japanese Patent Application Laid-Open No. 5-288556.
According to the above patent publication, a ring-shaped gain waveguide 5711 is formed on a semiconductor substrate 5710 having an pn-junction and carriers are implanted into the gain waveguide 5711 from an electrode 5722 as shown in FIG. 50 of the accompanying drawings in order to generate a laser oscillation. Then, the laser beams that are propagating through the gain waveguide 5711 clockwise and counterclockwise are partly taken out and caused to interfere with each other in photo-absorption region 5717. Then, the interfering beams are taken out through another electrode 5723 as a photoelectric current to see the intensity of interference. In FIG. 50, reference numeral 5712 denotes a reflection surface, reference numerals 5713 and 5714 denote optical output surfaces and reference numerals 5718 and 5719 denote optical outputs.
Japanese Patent Application Laid-Open No. 57-43486 (U.S. Pat. No. 4,431,308) discloses a gyro which utilizes the change of the terminal voltage of a semiconductor laser device caused by rotation without taking out light to the outside of the device. Referring to FIG. 51, a semiconductor laser device 5792 comprises two electrodes 5790 and 5791 on the top and the bottom thereof, numeral 5793 denotes a condenser for blocking direct current, numeral 5794 denotes an output terminal, and numeral 5795 denotes a resistor. It is described that a semiconductor laser device serving as a laser device in a ring laser device is connected to a driving power source 5796 so that the frequency difference between the lights propagating clockwise and counterclockwise, which are generated when an angular velocity is given to the device, is detected in terms of the change of the terminal voltage of the laser device, as shown in FIG. 51.
Japanese Patent Application Laid-Open No. 4-174317 also teaches detecting the change of the terminal voltage of a laser device caused by rotation.
However, neither of the above publications could detect the rotation direction of an object. This is because beat frequencies become equal when angular velocities are equal, even if rotational directions are different.
However, since known ring laser type gyros such as the one as described above are not adapted to detect the sense of rotation itself and therefore the latter has to be determined by applying a dither (micro-oscillation) and determining the correlation of the dither and the obtained signal.
Additionally, in known ring laser type gyros, the oscillation frequencies are separated from each other as the gyro rotates. The difference of the oscillation frequencies is very small when the rate of revolution is low and then there arises a locking-in phenomenon where the oscillation frequencies are led to one of the modes of oscillation. This locking-in phenomenon observable in known ring laser type gyros can be avoided by applying a dither.
Thus, it is the object of the present invention to provide a gyro that can detect the sense of rotation without using a mechanical device such as a dither generator.
According to the invention, the above object is achieved by providing a gyro comprising:
a laser device for generating laser beams to be propagated circuitally in opposite directions, wherein an electric signal is taken out from said laser device;
the oscillation frequencies of the laser beams being different from each other when said laser device is held stationary.
According to the invention, there is also provided a gyro comprising:
a laser device having an optical waveguide including an asymmetrically tapered region arranged at least in part thereof, wherein an electric signal is taken out from said laser device.
Said waveguide of the laser device may be ring-shaped and said asymmetrically tapered region may be arranged outside or inside the ring-shape.
Said tapered region of the optical waveguide may include a first tapered section gradually broadening the optical waveguide along the direction of laser beam propagation and a second tapered section gradually narrowing the optical waveguide along the direction of laser beam propagation.
The angles defined respectively by said first and second tapered regions and the region of the optical waveguides showing a constant width may be acute.
According to the invention, there is also provided a gyro comprising:
a laser device for generating laser beams to be propagated circuitally in opposite directions; and
an electric signal detection means for taking out an electric signal from said laser device;
the oscillation frequencies of the laser beams being different from each other when said laser device is held stationary.
Said electric signal detection means may comprise an electric terminal.
Said electric signal detection means may be a voltage signal detection means.
Said electric signal detection means may comprise a frequency-voltage conversion circuit.
Said electric signal detection means may comprise a subtraction circuit.
According to the invention, there is also provided a gyro comprising:
a laser device; and
a beat signal detection means;
said laser device having an optical waveguide including an asymmetrical tapered region arranged at least in part thereof.
According to the invention, there is also provided a gyro comprising:
a laser device for generating first and second laser beams; and
an optical detector for detecting the interfered light generated by interference of said first and second laser beams;
the oscillation frequencies of the first and second laser beams being different from each other when said laser device is held stationary.
According to the invention, there is also provided a laser device comprising:
an optical waveguide including an asymmetrically tapered region projecting to the outside;
said tapered region including a first tapered section gradually broadening the optical waveguide along the direction of laser beam propagation and a second tapered section gradually narrowing the optical waveguide along the direction of laser beam propagation;
the angles defined respectively by said first and second tapered regions and the region of the optical waveguides showing a constant width may be acute.
A gyro according to the invention may be arranged in a camera, a lens unit, an automobile, an aircraft or a ship.